/*
 * Copyright (C) 2011 The Guava Authors Licensed under the Apache License,
 * Version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law
 * or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

package com.andrew.apollo.utils;

/**
 * A time source; returns a time value representing the number of nanoseconds
 * elapsed since some fixed but arbitrary point in time. Note that most users
 * should use {@link Stopwatch} instead of interacting with this class directly.
 * <p>
 * <b>Warning:</b> this interface can only be used to measure elapsed time, not
 * wall time.
 * 
 * @author Kevin Bourrillion
 * @since 10.0 (<a
 *        href="http://code.google.com/p/guava-libraries/wiki/Compatibility"
 *        >mostly source-compatible</a> since 9.0)
 */
public abstract class Ticker {

    /**
     * Constructor for use by subclasses.
     */
    protected Ticker() {
    }

    /**
     * Returns the number of nanoseconds elapsed since this ticker's fixed point
     * of reference.
     */
    public abstract long read();

    /**
     * A ticker that reads the current time using {@link System#nanoTime}.
     * 
     * @since 10.0
     */
    public static Ticker systemTicker() {
        return SYSTEM_TICKER;
    }

    private static final Ticker SYSTEM_TICKER = new Ticker() {
        @Override
        public long read() {
            return System.nanoTime();
        }
    };
}
